Daynov: Played 3 for a tad more than 100 hours - thought it was a boring mess, but somehow I had to get my money's worth (being a dummy, bought it when it came out). New Vegas on the other hand I consider one of the best games in the past 10 years and arguably the best rpg to come out in a very long time (even with all the flaws the game has due the retarded engine it's built on).
If you thought it was a boring mess, I'd argue that "getting your money's worth" is not the appropriate term for spending 100 hours with it...
Out of curiosity: Did you mod the game?
Potzato: Playing F1 & F2 is not mandatory but it radically changes your perception (and experience) of F3 & NV. For bad or for worse ....
Also, I think if you had to play 2 games out of the four, the 2 first would be a better choice. That's my opinion, but I dare think many people here would agree.
I hated F3 btw :)
I played all three. I liked all three. F3 played very differently from the first two, but I did not care. I modded it quite a bit (as I do with most Bethesda games) which might have changed my perception of the game.
I have yet to play NV; as for the first three Fallouts, I'd say try out all of them. If the style of F1&2 or F3 does not suit you, you will probably notice soon enough.